The application of carbon nanotubes (CNTs) in advanced electronics has been investigated for over a decade, at least in part because carbon nanotubes offer a combination of small size, high mobility, ballistic transport, large current density, and low intrinsic capacitance. Single-wall carbon nanotubes (SWNTs) have been used in various kinds of integrated circuits such as logic gates, ring oscillators, and decoders. However, due to the coexistence of both metallic and semiconducting nanotubes, the on/off ratio is typically small for the as-made transistors using a large number of nanotubes, and various techniques including electrical breakdown, stripe patterning, or using presorted semiconducting nanotubes have been implemented to boost the on/off ratio of transistors.
Carbon nanotubes have been used in radio frequency (RF) applications, including transistors operating in the gigahertz frequency range. The nanotubes typically used are grown by chemical vapor deposition (CVD), and include a mixture of metallic and semiconducting nanotubes. The presence of the metallic nanotubes causes leakage current in the off-state and results in low on/off ratios. Although for analog/RF application, the on/off ratio is not as crucial as for digital applications, low on/off ratio can still result in low efficiency for applications such as power amplifiers and degrade the transconductance (gm) and cutoff frequency (ft) of the RF transistors. In addition, mismatch between the high resistance of nanotubes and outside conductive elements with large capacitance, as well as difficulty of nanotube assembly and integration, have presented challenges for the practical use of carbon nanotube devices for high frequency electronics.